The present invention relates generally to semiconductor integrated circuits, and more particularly to charge pumps.
System designs are routinely constrained by a limited number of readily available power supply voltages (Vcc). For example, consider a portable computer system powered by a conventional battery having a limited power supply voltage. For proper operation, different components of the system, such as display, processor, and memory components employ diverse technologies which require power to be supplied at various operating voltages. Components often require operating voltages of a greater magnitude than the power supply voltage and, in other cases, a voltage of reverse polarity. The design of a system, therefore, includes power conversion circuitry to efficiently develop the required operating voltages. One such power conversion circuit is known as a charge pump. Charge pumps have been used as on-chip voltage generators capable of providing a voltage more positive than the most positive external supply or more negative than the most negative external supply. The demand for highly efficient and reliable charge pump circuits has increased with the increasing number of applications utilizing battery powered systems, such as notebook computers, portable telephones, security devices, battery-backed data storage devices remote controls, instrumentation, and patient monitors, to name a few.
Inefficiencies in conventional charge pumps lead to reduced system capability and lower system performance in both battery and non-battery operated systems. Inefficiency can adversely affect system capabilities e.g., limited battery life, excess heat generation and high operating costs. Examples of lower system performance include low speed operation, excessive operating delays, loss of data, limited communication range, and inability to operate over wide variations in ambient conditions including ambient light level and temperature.
In addition to constraints on the number of power supply voltages available for system design, there is increasing demand for reducing magnitudes of the power supply voltages due to shrinking die size and also to save power. The demand in diverse application areas requires highly efficient charge pumps that operate from a supply voltage of around one volt.
Thus, there is a need for a low voltage charge pump that can operate at supply voltages less than one volt while reducing the die area and increasing the power efficiency.
In accordance with the present invention, a charge pump for providing a higher output voltage relative to an input or supply voltage includes a charge storage device or main pump capacitor. A pre-charge circuit is included for pre-charging the charge storage device to a charge level to provide a predetermined output voltage from the charge pump. A blocking circuit is also provided to prevent charge leakage from the charge storage device to the pre-charge circuit.
In a further embodiment of the present invention, a method for making a charge pump includes forming a charge storage device; forming a pre-charge circuit for charging the charge storage device to a charge level to provide a predetermined output voltage from the charge pump; and forming a blocking circuit to prevent charge leakage from the charge storage device to the pre-charge circuit.